In the related art, a seat slide apparatus for a vehicle includes lower rails which are fixed to a vehicle floor, and upper rails which are slidably engaged with the lower rails and support a seat at an upper side thereof. The seat slide apparatus enables the seat to be moved forward and rearward by sliding the upper rails relative to the lower rails.
For example, in a seat slide apparatus disclosed in WO 2010/024210A (Reference 1), a rolling element circulation unit is provided to be interposed between a lower rail and an upper rail. The rolling element circulation unit includes a case which defines an annular accommodating path, and a plurality of rolling elements which is accommodated in the annular accommodating path. In addition, in the rolling element circulation unit, each of the rolling elements is exposed through an opening formed in the case, and thus is in contact with an inner wall surface of the lower rail. Further, the rolling element circulation unit is configured such that when the upper rail slides relative to the lower rail, each of the rolling elements rolls in the annular accommodating path, and as a result, the upper rail may smoothly move forward and rearward.
In addition, for example, in a seat slide apparatus disclosed in JP 2015-003591A (Reference 2), an upper rail includes a pair of sidewall portions which face each other in a width direction, and an upper wall portion which connects the upper ends of the sidewall portions. In addition, the upper rail has a folded-back portion which is folded back outward in a rail width direction from the lower end of each of the sidewall portions, and extends upward. Further, the seat slide apparatus includes rolling elements retained between a tip end portion of each of the folded-back portions and an inner wall surface of a lower rail.
Typically, the rolling elements in the seat slide apparatus are interposed between the upper rail and the lower rail in a state in which each of the rolling elements is in contact with an outer surface of the upper rail formed by the folded-back portion and the inner wall surface of the lower rail at two positions spaced apart from each other in a vertical direction when viewed in a cross section orthogonal to a longitudinal direction of the lower rail and the upper rail. However, in the configuration, when a seat load applied to the seat is applied to the upper rail, the folded-back portion is warped inward with respect to the lower rolling elements acting as support points. Therefore, gaps may be formed between the rolling elements and the folded-back portion of the upper rail and between the rolling elements and the inner wall surface of the lower rail, and as a result, there is a concern that rattling occurs.
However, in the configuration of Reference 2, the folded-back portion is lifted upward with respect to the lower rolling elements acting as support points when a seat load is applied to the upper rail. That is, the folded-back portion of the upper rail presses the rolling elements retained at the tip end surface of the folded-back portion against the inner wall surface of the lower rail. Therefore, it is possible to suppress the problem concerning the gaps formed between the rolling elements and the inner well surface of the lower rail and between the rolling elements and the folded-back portion of the upper rail based on the seat load.
However, it is difficult to apply the configuration of the seat slide apparatus provided with the rolling element circulation unit that accommodates the plurality of rolling elements in the case as disclosed in Reference 1 to the configuration of the seat slide apparatus in which the rolling elements are retained at a tip end portion of the folded-back portion that extends upward as disclosed in Reference 2. For this reason, the problem concerning the gaps between the rolling elements and the folded-back portion of the upper rail and between the rolling elements and the inner wall surface of the lower rail may still occur in the configuration including the rolling element circulation unit, and as a result, there is a need for improvement.
Thus, a need exists for a seat slide apparatus for a vehicle which is not susceptible to the drawback mentioned above.